If anything, it seems like Optimus Prime is leading a charge AT us and Megatron (clearly not firing anywhere Prime is or was) is giving him cover fire. Seekers provide air support while Shockwave falls prey to Rob Liefeld Smoke eating his foot.
(Hot Rod notably took the battle TO Unicron -- still an immense unknowable threat -- in the Movie, armed only with the knowledge that the Matrix would do... something, in a foolhardy heroic charge, just like his dad Optimus. The latter's sacrifice is iconic for a reason. A siege on Autobot City by the Decepticons, who have a head start, AND a Devastator who easily clowns the Autobots' heaviest hitters, would seem to also call for a tactical retreat. And yes, not calling for that tactical retreat contributed to Optimus Prime getting killed because of Hot Rod amirite. But while falling back to protect others and regroup for a more likely strategic victory is no less a heroic act for its avoidance of conflict at the moment, it's still fair to expect heroes to rise to the occasion.)
I mean, are they even running FROM Unicron? Unicron isn't even facing them. He's drunkenly drifting amid a bunch of explosions but he might even just float past the horizon while his outer ring is having a stroke. He's like a Jeff Lee Johnson painting, more weirdness shows up the more you look.
(apologies for the edits, my post was also like a Jeff Lee Johnson painting)